The present invention relates to the field of “benthic barriers,” so called because they are barriers to the bottom of an area of water. The benthic zone is the ecological region at the lowest level of a body of water such as a lake, including the sediment surface and some sub-surface layers. Such barriers are typically placed in “photic zones,” which are areas where enough sunlight reaches the benthic area to permit photosynthesis, allowing aquatic plant growth. Benthic Barriers are intended to block sunlight from reaching lake bottoms, thereby preventing photosynthesis and eliminating unwanted, aquatic plant growth in specific areas where benthic barriers are placed.
Know by common names such as, “lake weed control mats,” “seaweed mats” and simply, “weed mats,” crude versions of benthic barriers have been used in the United States for well over 100 years. Early benthic barriers were first fashioned of materials such as burlap and canvas to block sunlight and were held on the bottom primarily with rocks. Primitive frames were sometimes constructed with iron bars car fencing to, hold the fabrics in place. In some mats, metal bars, like reinforcing rod, have been placed transversely across the mat. Others attach frames on the perimeter of the fabric. Remarkably, many homemade frames were made of wood (which floats). Other frames have been fashioned from steel reinforcing rod, which is a soft, flexible bar, with a very low “bend moment.”
Some of these barriers today comprise a polymeric fabric mat. In some, the polymeric fabric mat is surrounded by a rectangular frame to which the mat is secured. Some mats include small gas relief openings in the body of the mat, so that gas coming up from beneath the mat can escape through those openings. A mat sold by Lacey Inc. is provided with semi-circular slits in the mat, to define openings with adjacent flaps. This allows the mats to settle to the bottom of the lake more quickly, and also facilitates the escape of gas which tends to bubble up beneath the mat and lift the flaps out of the way.